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How can you measure how many people are modern slaves?

In this post, Professor Kevin Bales, one of the lead educators on the University of Nottingham’s course Ending Slavery, looks at how we can best measure global slavery.

In this post, Professor Kevin Bales, one of the lead educators on the University of Nottingham’s course Ending Slavery, looks at how we can best measure global slavery.

How many people around the world do you think are victims of slavery today? Modern slavery is a hidden crime that is especially hard to measure. That’s why a group of researchers came together to develop the Global Slavery Index, which measures slavery as accurately as possible. The 2016 Global Slavery Index estimates there are 45.8m people worldwide in slavery today. That is more than the entire population of Canada, Poland, Uganda or Malaysia.

Modern Slavery FutureLearn
One of a group of young women trafficked into a sweatshop who were forced to worked 20 hours a day with no pay and very little food. After escaping and being taken in by a shelter in Bangkok, she eventually felt able to tell her story resulting in a police raid that freed 38 other women. Kay Chernush for the U.S. State Department

Counting a crime

Like victims of sexual assault, victims of slavery feel stigma and shame, in part because sexual assault is very common in slavery cases. As a result, they are unlikely to report it to the authorities so the crime goes unrecorded. But slavery also defies measurement for a unique reason.

Normally, to determine the level of any specific crime in developed countries, the results of a national sample crime survey are compared to the official arrest and conviction rate. When being counted, all crimes are treated as “events”, also known as short single episodes.

But slavery is a crime which starts, and then continues for an indeterminate time – for days, months, or even years. This unique fact about slavery crime means it can rarely be measured using national crime surveys, as the victim is hidden away, enslaved, and not available to answer questions.

Understanding slavery

In an attempt to measure the incidence of slavery with greater accuracy, the Global Slavery Index casts the net wide. Instead of just individuals, it surveys households and families to see if anyone knows someone who has experienced slavery.

These surveys provide an estimate of the proportion of the population who are enslaved, and include cases that happened in other countries. For example, respondents in national surveys in Nepal identified significant numbers of family members enslaved in Qatar and other Gulf States.

The household surveys work well in countries in the developing world, but in North America and Europe more active law enforcement means criminals work hard to keep their slaves hidden. Fortunately, a statistical technique called multiple systems estimation (MSE) can provide reliable estimates of these hidden populations.

First used to estimate the number of fish in a Swedish fjord, MSE has been regularly used to determine the number of civilian deaths in ongoing conflicts. It works by comparing lists of casualties from hospitals, police and families, to determine an estimate of the total killed. When applied to slavery, it creates an estimate by comparing the lists of victims known to different agencies, such as the police, non-governmental organisations (NGOs), and social service providers.

The UK was the first country to use this technique to estimate slavery, in late 2014, and immediately revised its official figures upwards from the 2,744 cases that were known to exist to an estimated 10,000 to 13,000 slaves. That remains the estimated figure today, and was quoted by the Prime Minister of the UK in her announcement of a new taskforce and fund to tackle modern slavery. It is a figure I developed with the Chief Scientific Advisor to the Home Office, Bernard Silverman.

As the modern antislavery movement pushes forward, these new breakthrough methods mean there is a yardstick to gauge the progress of liberation. This is important because you can’t solve a problem you can’t understand. Having a metric is crucial if we are to take effective action.

Knowing the geographical spread of slavery also brings with it knowledge of which products and commodities might be tainted by bondage – for example, the minerals in our phones and laptops may well have been extracted from the ground by slaves. And as the estimates become more precise, governments, NGOs, and international bodies can mark their progress, allowing us to trace the best roads to freedom.

At the University of Nottingham, we are looking at how to end slavery worldwide in our online course, Ending Slavery (starting 17 October). On it you’ll learn from experts at the cutting edge of contemporary slavery research, investigating the complex systems that sustain slavery today. Together we will figure out what individuals, communities, governments, companies and the international community should do next.

Join Ending Slavery and find out how you can make a difference to this major human rights issue.


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